feat(images): two-line boot-screen footer for the PR title

nixos/_images/base/iso.nix

@@ -35,53 +35,70 @@
   boot.loader.systemd-boot.enable = lib.mkForce false;
   boot.loader.efi.canTouchEfiVariables = lib.mkForce false;
 
-  # ── Show the build identity on the boot screen as a footer label ─────────────
+  # ── Show the build identity on the boot screen as a footer ───────────────────
   # The boot-menu ENTRY can't carry the build identity: it's a single,
   # non-wrapping line in a fixed-width GRUB/isolinux menu, so a long PR title
   # overflows and gets clipped (and widening the menu makes it span the whole
-  # screen). Instead, render coderBox.bootLabel — e.g.
-  # "Coder Box - PR #46: <title> (abc123@branch)", or just
-  # "Coder Box - abc123@branch" with no PR — as a standalone GRUB *label*
-  # (boot-screen chrome, not a selectable entry) shown as a footer UNDER the menu.
-  # The label is ALWAYS present (every build has a commit/branch), so this also
-  # makes the footer visible on local/non-PR builds, not just CI PR previews.
+  # screen). Instead, render the identity as standalone GRUB *labels*
+  # (boot-screen chrome, not selectable entries) shown as a footer UNDER the
+  # menu, on up to two lines so a long PR title doesn't overflow the width:
+  #   line 1 (always):  "Coder Box - <short-sha>@<branch>"
+  #   line 2 (PR only): "(PR #46: <title>)"
+  # Line 1 is always present (every build has a commit/branch), so the footer
+  # shows on local/non-PR builds too, not just CI PR previews.
   #
   # Key gotcha: the stock theme's boot_menu fills almost the whole height with an
   # opaque white pixmap (boot_menu_*.png), and GRUB paints that box OVER any
   # label that overlaps it — so a footer placed inside the box is invisible. The
   # menu only has a handful of entries, so we shrink boot_menu's height to free
-  # the lower area of the screen, then place the label there on the plain
+  # the lower area of the screen, then place the labels there on the plain
   # background (dark text, good contrast). The menu WIDTH is untouched (still the
-  # stock 800px), so the menu doesn't blow up horizontally like the earlier
-  # full-width experiment. EFI/GRUB only; the BIOS/isolinux text menu has no
-  # theme, so there the identity is available off-menu via /etc/coder-box-pr +
-  # the installer console banner.
+  # stock 800px), so the menu doesn't blow up horizontally. EFI/GRUB only; the
+  # BIOS/isolinux text menu has no theme, so there the identity is available
+  # off-menu via /etc/coder-box-pr + the installer console banner.
   #
   # substituteInPlace uses --replace-fail so a future nixpkgs theme reflow fails
   # the build loudly instead of silently dropping the footer.
   isoImage.grubTheme =
     let
-      inherit (config.coderBox) bootLabel;
+      inherit (config.coderBox) bootLabelLine1 bootLabelLine2;
       # theme.txt wraps the text in double quotes; neutralise quotes/backslashes
       # so an arbitrary title can't break the theme parser.
-      bootLabelThemeSafe = builtins.replaceStrings [ "\"" "\\" ] [ "'" "" ] bootLabel;
+      themeSafe = builtins.replaceStrings [ "\"" "\\" ] [ "'" "" ];
+      line1 = themeSafe bootLabelLine1;
+      line2 = themeSafe bootLabelLine2;
+      # A GRUB `+ label` is a single line, so line 2 (the PR title) is a second
+      # label stacked ~1 line-height (font is 20px) below line 1. Only emitted
+      # for PR builds (bootLabelLine2 is empty otherwise).
+      line2Label = lib.optionalString (bootLabelLine2 != "") ''
+
+        + label {
+        	top = 50%+28
+        	left = 50%-400
+        	width = 800
+        	align = "center"
+        	color = "#232627"
+        	font = "DejaVu Regular"
+        	text = "${line2}"
+        }
+      '';
     in
     pkgs.runCommand "coder-box-grub2-theme" { } ''
       cp -r ${pkgs.nixos-grub2-theme} "$out"
       chmod -R u+w "$out"
 
       # 1) Shrink the menu box so its opaque pixmap stops at ~46% of the screen
-      #    (~1/3 shorter than the previous 62%), leaving the lower area free for
-      #    the footer (stock fills to the progress bar and would cover it).
+      #    (~1/3 shorter than the stock full height), leaving the lower area free
+      #    for the footer (stock fills to the progress bar and would cover it).
       substituteInPlace "$out/theme.txt" \
         --replace-fail 'height = 100%-3%-100-3%-3%-32-3%' 'height = 46%-100-6%'
 
-      # 2) Footer label just BELOW the shrunk box (top ~50%), so it sits close to
-      #    the menu rather than far down the screen. Its left/width match the menu
-      #    box (left = 50%-400, width = 800) so the centred text lines up with the
-      #    rectangle instead of spanning the full screen. Quoted heredoc so the
-      #    build shell does no expansion; the text is already substituted by Nix
-      #    (and quote/backslash-sanitised).
+      # 2) Footer label(s) just BELOW the shrunk box (top ~50%), so they sit close
+      #    to the menu. left/width match the menu box (left = 50%-400, width =
+      #    800) so the centred text lines up with the rectangle. Quoted heredoc so
+      #    the build shell does no expansion; the text is already substituted by
+      #    Nix (and quote/backslash-sanitised). line2Label is empty on non-PR
+      #    builds.
       cat >> "$out/theme.txt" <<'EOF'
 
       + label {
@@ -91,8 +108,8 @@
       	align = "center"
       	color = "#232627"
       	font = "DejaVu Regular"
-      	text = "${bootLabelThemeSafe}"
-      }
+      	text = "${line1}"
+      }${line2Label}
       EOF
     '';
 

nixos/_images/box-turnkey.nix

@@ -69,11 +69,13 @@ let
   # "<short-sha>@<branch>" form (branch omitted when unknown/detached).
   versionStamp = revShort + lib.optionalString (branchClean != "") "@${branchClean}";
 
-  # Boot-screen label (the GRUB footer in ../base/iso.nix). ALWAYS present so the
-  # image's identity is visible on the boot screen regardless of build type:
-  #   with a PR:    "Coder Box - PR #46: <title> (<short-sha>@<branch>)"
-  #   without a PR: "Coder Box - <short-sha>@<branch>"
-  bootLabel = "Coder Box - " + (if prFull != "" then "${prFull} (${versionStamp})" else versionStamp);
+  # Boot-screen footer (the GRUB label(s) in ../base/iso.nix), rendered on up to
+  # two lines so a long PR title doesn't overflow the screen width:
+  #   line 1 (always): "Coder Box - <short-sha>@<branch>"
+  #   line 2 (PR only): "(PR #46: <title>)"
+  # A non-PR build shows only line 1.
+  bootLabelLine1 = "Coder Box - ${versionStamp}";
+  bootLabelLine2 = lib.optionalString (prFull != "") "(${prFull})";
 in
 {
   imports = [
@@ -146,15 +148,22 @@ in
     description = "Full PR identity (number + untruncated title) for off-menu surfaces (empty for non-PR builds).";
   };
 
-  # Boot-screen label (the GRUB footer in ../base/iso.nix), e.g.
-  # "Coder Box - PR #46: <title> (abc123def456@my-branch)" or, without a PR,
-  # "Coder Box - abc123def456@my-branch". Always non-empty.
-  options.coderBox.bootLabel = lib.mkOption {
+  # Boot-screen footer, split across up to two GRUB labels (../base/iso.nix):
+  #   line 1 (always):  "Coder Box - abc123def456@my-branch"
+  #   line 2 (PR only): "(PR #46: <title>)"  (empty string on non-PR builds)
+  options.coderBox.bootLabelLine1 = lib.mkOption {
     type = lib.types.str;
     internal = true;
     readOnly = true;
-    default = bootLabel;
-    description = "Boot-screen footer label (build identity: PR + short-sha@branch); always present.";
+    default = bootLabelLine1;
+    description = "First boot-screen footer line (Coder Box - short-sha@branch); always present.";
+  };
+  options.coderBox.bootLabelLine2 = lib.mkOption {
+    type = lib.types.str;
+    internal = true;
+    readOnly = true;
+    default = bootLabelLine2;
+    description = "Second boot-screen footer line ((PR #N: title)); empty on non-PR builds.";
   };
 
   config = {